Studs are required where maximum gasket loading & reduced wear and tear on the block threads are desired. Aircraft quality 8740 chrome moly steel is used to produce premium grade, race quality fasteners. Ground and thread rolled after heat treat to assure exacting tolerances. 190,000 PSI tensile strength is equal to the most demanding of applications. Kits include 4130 heat treated, parallel ground washers and high strength nuts. The Milodon name is your assurance of quality and a part warranted 100% unbreakable. Sold in complete 2 heads sets. Made in USA.